linux-kernel - [PATCH] fs: add RWF

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Date:   Sat,  9 Sep 2017 10:23:49 +0200
From:   Jürg Billeter <j@...ron.ch>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jürg Billeter <j@...ron.ch>
Subject: [PATCH] fs: add RWF_APPEND

This is the per-I/O equivalent of O_APPEND to support atomic append
operations on any open file.

On Linux, if a file is opened with O_APPEND, pwrite() ignores the offset
and always appends data to the end of the file. RWF_APPEND enables
atomic append and pwrite() with offset on a single file descriptor.

Signed-off-by: Jürg Billeter <j@...ron.ch>
---
 include/linux/fs.h      | 2 ++
 include/uapi/linux/fs.h | 6 +++++-
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index e723b62c4b81..5f27ef9cce17 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3187,6 +3187,8 @@ static inline int kiocb_set_rw_flags(struct kiocb *ki, rwf_t flags)
 		ki->ki_flags |= IOCB_DSYNC;
 	if (flags & RWF_SYNC)
 		ki->ki_flags |= (IOCB_DSYNC | IOCB_SYNC);
+	if (flags & RWF_APPEND)
+		ki->ki_flags |= IOCB_APPEND;
 	return 0;
 }
 
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index ea84938da405..5477480d0502 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -330,7 +330,11 @@ typedef int __bitwise __kernel_rwf_t;
 /* per-IO, return -EAGAIN if operation would block */
 #define RWF_NOWAIT	((__force __kernel_rwf_t)0x00000008)
 
+/* per-IO O_APPEND */
+#define RWF_APPEND	((__force __kernel_rwf_t)0x00000010)
+
 /* mask of flags supported by the kernel */
-#define RWF_SUPPORTED	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT)
+#define RWF_SUPPORTED \
+	(RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT | RWF_APPEND)
 
 #endif /* _UAPI_LINUX_FS_H */
-- 
2.14.1